This invention concerns magnetic drives, particularly but not exclusively for valves for controlling gas flow or fluid flow and for opening and closing electrical switch contacts.
Magnetic attraction and repulsion is commonly employed as a motive force to operate devices such as valve closure members, pistons in cylinders to achieve a pumping action, and contactors and switches for opening and closing electrical circuits.
Such drives may have a bistable or monostable characteristic, and often employ a spring force to provide a restoring force and create a monostable operating characteristic.
Magnetic fields to achieve the operation are usually generated by causing an electric current to flow in a winding surrounding a ferromagnetic core or the like, which if the magnetic field is to collapse when the current flow ceases (as is usually required), is usually constructed from a magnetisable material having a low magnetic permanence.
Where valves control the flow of inflammable or poisonous gases or fluids, it is usual to design the magnetic drive therefor to be monostable and to have a so-called fail-safe characteristic in the event of a power failure. By fail-safe is meant that the valve will revert to a closed condition in the event that there is an electrical power failure.
The invention seeks to obviate the need to provide electric current continuously to maintain the operational state of a monostable device.
It is a particular object of the present invention to provide a bistable magnetic drive which does not require a continuous current flow to maintain it in either of its stable states.
Another object of the present invention is to provide a magnetic drive having a bistable characteristic, which can be readily modified to possess a monostable characteristic so that it will revert to (or remain in) one of its two states in the event of a power failure.
It is a further object of the invention to provide a mechanical device for altering the characteristics of a bistable magnetic device, to those of a monostable device.
It is a still further object of the invention to provide a digital fluid flow controlling valve, particularly for controlling the flow of gas or air.
It is a still further object of the invention to provide a digitally controllable gas flow control valve with a safety characteristic which reverts to a closed state in the event of the failure of a monitored source of energy such as an electrical current flow, a source of heat, or a source of light.
A further object of the invention is to provide pneumatic devices in which air or gas flow is under the control of valves controlled by such improved magnetic drives.
From U.S. Pat. Nos. 4,554,610, 4,386,823 and 3,772,540 are known magnetic drive devices having permanent magnet means, an armature displaceable between air gaps and an electromagnetic winding for driving the armature. In all cases, the axis of the winding lies parallel to the path of movement of the armature.
According to one aspect of the invention a magnetic drive device comprises a permanent magnet means generating magnetic flux, an armature mounted for movement enabling it to occupy either a first air gap in which the flux is in one direction, or a second air gap in which the flux is in the opposite direction, with a region of flux cancellation between the two air gaps, and at least one electromagnet winding having an axis generally perpendicular to the path of movement of the armature coil to which current can be supplied to adapt said at least one winding when energised to produce a magnetic flux in said one direction or the other, depending on the direction of the current, the flux from the winding increasing the flux density in the other air gap, thereby effectively shifting the flux cancellation region towards or into one of the two air gaps so as to produce a flux density gradient extending from one air gap to the other which will cause the armature to move into (or remain in) the air gap having the higher flux density, wherein the armature will continue to remain after the current flow ceases.
According to another feature of the invention, in use the winding both polarises the armature and changes the magnetic flux in the air gaps.
According to another aspect of the invention in a magnetic drive device as aforesaid further includes low reluctance flux concentrating means external to the electromagnet winding which provides a low reluctance external path for returning flux from one end to the other thereof when the winding is energised, thereby to increase the flux produced by the winding when energised, so as to magnify the magnetic flux available to effect movement of the armature.
The external flux concentrating means conveniently comprises at least one elongate member of magnetisable material which extends parallel to the magnetic flux in the air gap and generally perpendicular to the direction of movement of the armature and beyond the extent of its travel.
A magnetic drive device as aforesaid, (with or without the external flux concentrating means) may comprise four similar elongate magnetisable pole pieces arranged symmetrically in pairs, each pair occupying one of the two magnetic fields, wherein the air gap between the pole pieces in each pair defines the air gaps at the two extremes of the armature travel, and the two pairs of pole pieces serve to concentrate the internal magnetic flux into the two air gaps at opposite ends of the armature travel.
The combination of internal and external flux concentrating elements assists in defining the two stable positions of the armature and also assists in effecting the movement of the armature from one end to the other.
A pair of electrical contacts may be provided at one end of the armature travel which are electrically joined by being bridged by the armature, or by conductive means or a coating on the armature, when the latter is located at that end of its travel.
Likewise a pair of electrical contacts may be provided at the other end of the travel as well, and if required second conductive means or a coating is provided on the armature to ensure that the said other contacts are also bridged when the armature is at the other end of its travel.
By providing electrical contacts at either one or both ends of the armature travel, the drive is converted into an electrical switch in which one pair of contacts are bridged when the armature is at one end of its travel and the other pair are bridged when it is at the other end of its travel. The converted drive is therefore equivalent to an electromagnetic relay or contactor.
According to a further aspect of the invention a magnetic drive device as aforesaid may be contained within a sealed chamber and where electrical contacts are involved, at least part of the wall of the chamber may be formed from electrical insulating material to provide a region for conductive feedthroughs to terminals external of the chamber to allow electrical connection to be made to the contacts therein which, when the armature is in an appropriate position, are bridged thereby.
The chamber for example may be formed from plastics or glass or quartz.
According to another aspect of the invention, a magnetic drive device as aforesaid may include a further flux concentrator which is movable relative to the drive, so as to adopt a first position relatively close to the drive to reduce the flux density at one end of the armature travel, thereby causing the device to assume a monostable characteristic when the further concentrator is in that position, and is movable out of the first position into a second position where it has little or no influence on the flux density in the drive, to reinstate the bistable characteristic of the drive.
In an alternative arrangement, the said further flux concentrator may be permanently located very close to one end of the armature travel so as to produce a drive having a permanent monostable characteristic.
In one embodiment of the invention, a single permanent magnet may be employed at one end of an electromagnetic coil having located internally thereof two pairs of aligned, spaced apart pole pieces, defining air gaps at opposite ends of the armature travel, with or without external flux concentrating elements for increasing the flux density attributable to a current flowing in the electromagnetic coil, and instead of a second permanent magnet being located at the opposite end of the coil, an elongate member of magnetisable material is provided formed from material similar to that from which the pole pieces are formed, such that flux issuing from one of the two nearer internal pole pieces passes into and through the magnetisable material to issue from the other end thereof and pass into the other of two nearer internal pole pieces.
The elongate magnetisable member thus provides a return path for the flux and maintains the flux direction at each end of the armature travel in the same way as a second permanent magnet would have done, and thus removes the need for a second permanent magnet.
Further flux concentration can be obtained by providing field focusing pole pieces at opposite ends of the permanent magnet, and magnetisable elements at the opposite end of the coil (or at each end of the two permanent magnets where permanent magnets are located at both ends of the coil), wherein the pole pieces extend laterally of each magnet or length of magnetisable material and extend towards the pole pieces and flux concentrating elements located externally of the coil where provided.
In such an arrangement, any said further concentrator which is employed to produce a monostable characteristic in the drive, may also include pole pieces for fitting with small air gaps, between the said field focusing pole pieces and any internal pole pieces, and/or any external concentrator(s), at opposite ends of the coil.
An energy storing device such as spring means may be provided at one end of the armature travel, which absorbs energy derived from the final movement of the armature into its rest position at that end of its travel.
Preferably an energy storing device is located at both ends of the armature travel.
The stored energy in such an arrangement acts to accelerate the armature out of its rest position when a current flows in the electromagnetic winding causing the flux to collapse in the air gap occupied by the armature. This assists in the change of state of the device.
The invention also lies in a magnetic drive device which comprises magnet means producing first and second magnetic fields, the polarity of the first and second fields being opposite, and a magnetisable armature mounted for movement between the two said fields, the armature being magnetised South/North or North/South depending on which of the two fields it occupies and requiring considerable force acting perpendicular to the magnetic flux lines to shift the armature out of the influence of either field once it is aligned therewith, and a magnetic or magnetisable shunt is provided which is movable into a position in which the magnetic flux of one of the first and second fields becomes diverted therethrough, so as to cause the armature to either remain in the unaffected field or immediately to move, under the influence of the unaffected magnetic field flux, so as to occupy the unaffected field.
Shifting the armature from one end to the other of the device may be achieved by depleting the magnetic flux at the said one end and/or reinforcing the flux at the said other end. This may be achieved by causing an electric current to flow in an energising winding, which is located so as to influence the flux in one or other or both of the two fields. Two such windings may be provided or by movement into the vicinity of the device of a magnetised member or member of magnetisable material.
The armature is generally formed from magnetisable material, typically a ferro-magnetic material, and in order to reduce its mass, a split form of construction may be employed in which ferro-magnetic poles are located at opposite ends of the drive with a relatively small gap between the opposed magnetic pole faces, and the movable portion of the armature (also formed from magnetisable material) is designed so as just to fit in the small gaps between the opposed pole faces at the opposite ends of the drive, the movable element itself being secured to one end of a connecting rod which extends through one end of the magnetic drive to terminate externally of the drive in a valve closure member.
By constructing the armature in this way, the mass of the armature can be reduced to little more than the mass of the connecting rod, which itself can be hollowed so as to reduce its mass, and the solid piece of ferro-magnetic material forming the movable part of the armature is simply a small cross-section, but solid extension, of the connecting rod.
The connecting rod is preferably formed from non-magnetic material.
By reducing the mass of the armature in this way, the operating speed of the device (and any valve associated therewith) can be increased considerably relative to an arrangement in which a more massive armature has to be moved from one end of the drive to the other under the influence of the same magnetic field gradient.
Any of the magnetic devices as aforesaid may serve to operate a valve for controlling the flow of gas or air or liquid or provide the movement necessary to open and close electrical contacts of an electrical switch.
If a magnetic shunt is provided which is permanently in position, then it can be arranged that either the additional flux provided by the energising winding will be sufficient to overcome the non-shunted field at the other end of the device, or not to do so. If the induced flux is sufficient to move the armature from the non-shunted field into the shunted field, it will be seen that as soon as the energising current is removed (or significantly reduced), the armature will return to the non-shunted field end.
Another arrangement is one in which an additional electro-magnetic device is provided at the shunted field end of the device, with which the armature makes contact when moved into the shunted field. Preferably the additional device includes a magnetic core and the contact with the armature means that there is no air gap to reduce the flux density after contact is made. By providing a complete magnetic path without an air gap, the flux density is magnified many times. This arrangement therefore enables the armature to be attracted away from the non-shunted field by a high electric current flowing in the additional device, which can be reduced to a low current once the armature and device core make contact to hold the armature at the shunted field end.
Such an arrangement has a fail-safe characteristic in that if the small holding electric current fails, the residual flux gradient present in the drive will be such as to cause the armature immediately to move to occupy the non-shunted field where the static flux is highest.
The additional electromagnetic device may be a solenoid having a large number of turns on a magnetic corexe2x80x94eg a core of ferromagnetic material, so that only a small current will still produce a high magnetic flux.
A valve employing a magnetic drive device as aforesaid may be used for example to control the flow of inflammable gas to a burner or jet, wherein a thermocouple is located adjacent the burner or jet so as to be heated by a flame emanating therefrom to cause electric current to flow in any circuit connected to the thermocouple. Thus if the latter either produces, or controls the production of, a current for the holding solenoid at the shunted field end, the solenoid will produce a magnetic flux sufficient to retain the armature in contact therewith at the shunted field end provided the thermocouple remains heated by the flame. In the event of flame failure for any reason, the thermocouple cools, the holding current collapses and with it the magnetic flux linking the holding solenoid to the armature, thereby releasing the latter to move to the higher flux concentration at the other end of its travel.
An alternative arrangement which has similar fail-safe characteristics involves mounting the flux short circuiting device on a movable element, the position of which relative to the drive is controlled by the passage of an electric current or is dependent upon a particular voltage being present, or a gas or fluid pressure being exerted against the movable element, or any other physical parameter which changes in the event of some failure (such as flame failure in a gas burner) which will result in the movable element shifting the flux shunting device from a position in which a relatively large air gap exists between it and the magnetic flux at one end of the drive, into a position in which the shunting element diverts most or all of the said flux to significantly reduce the flux density at that end of the armature travel and cause the armature either to move to the other end of the drive to where the magnetic flux remains unaffected, or to remain at that other end.
Preferred forms of movable element are a bimetal strip, a piezo bender, a spring, a diaphragm or other device which will move under increasing or decreasing pressure.
In addition or instead of movement in relation to failure of a flame or other physical event, the mechanism which determines the instantaneous position of the flux shunting element can be adapted to respond to an increase in a monitored parameter such as temperature or pressure as well as a decrease. Thus the flux shunting device may be moved into position so as to direct the flux at one end of the drive, either in response to flame failure (in the case of a gas burner) or in the event of excess temperature.
Where a holding solenoid is to be provided, this may be located to advantage within the drive, at the end which is to be affected by the flux shunting element.
A magnetic device as described may be combined with a chamber to or from which fluid can flow depending on the position of a valve closure member relative to a valve seating surrounding an opening, which in one end position of the armature travel is closed by the valve closure member, and in the other end position of the armature travel, is unobstructed by the valve closure member.
In such arrangements it may be necessary to ensure that there is no chance of leakage of the fluid (which may be gas or liquid), into the device. This is particularly important where a flammable or explosive gas or liquid is involved. To this end the opening through which the connecting rod extends, between the magnetic drive and the valve closure member, may be sealed with one or more seals to prevent the escape of fluid (gas or liquid) from the chamber.
More preferably a diaphragm seal may be provided, instead of or in addition to sealing means surrounding the connecting rod, and the diaphragm material is selected so as to be impervious to the fluid to be controlled and is sufficiently flexible to permit linear movement of the connecting rod in response to movement of the magnetic armature.
In a preferred arrangement the diaphragm is generally circular in shape, includes a corrugated annular region to provide flexibility and permit movement of its central region relative to the circumference thereof, and is centrally perforated to allow the connecting rod to extend therethrough, but is sealed around the connecting rod, typically to a collar on the rod, the collar forming an integral part of, or being sealingly fitted to, the rod, and the periphery of the diaphragm is likewise bonded or otherwise sealingly joined to a larger diameter collar which is sealingly joined or integrally formed with an end wall of the magnetic drive assembly, which forms at least part of one wall of the fluid chamber into which the connecting rod and valve closure member extends.
When combined with a fluid containing chamber as aforesaid, and a flux shunting element is provided at one end of the drive device, typically the end thereof remote from the fluid chamber, a button operated setting/resetting device may be provided, proximate to the flux shunting element, for holding the latter away from the magnet assembly while the bimetal strip, piezo bender, or other mechanism which will normally hold the flux shunting element away from the magnetic field, establishes a sufficient force to stand off the flux shunting element after the button is released.
In addition or alternatively, an emergency button may be provided for forcing the flux shunting element into contact with the magnet components of the device to cause the valve to flip into its closed condition as a consequence of the collapse of the magnetic flux, in one of the fields.
Typically the collapse occurs in the field remote from the fluid chamber containing the valve closure device.
According to a further aspect of the invention, an array of a plurality of bistable flow control valves is provided associated with orifices which differ in size, and control means select different ones of the orifices to be open, either alone, or in combination with others, so that a range of differently sized openings through the array can be obtained, so as to regulate the flow of fluid there, the opening size being determined by the particular orifices which are open and in turn determining the rate of flow therethrough (for a given pressure differential), wherein each valve closure member is controlled by a magnetic drive device as aforesaid.
Preferably the different areas of the orifice openings which can be obtained, constitute each of a sequence of opening areas such that a progression of areas from zero to a maximum area value (when all the valves are open), can be obtained in a series of discrete steps.
According to another aspect of the invention, a plurality of magnetic drive devices as aforesaid may be employed to open and close each of a corresponding plurality of valve closure members for controlling the exit of fluid under pressure from manifold constituting a reservoir thereof, and the electromagnet winding of each drive is selectively connectable to a source of electric current, and programmable control means may be provided to establish connections to the source of current and the direction of current flow in the windings. The control means may be under computer control, programmable to open and close the valves in a sequence, or one or more patterns, or in a sequence of patterns.
Each valve may be associated with an orifice through which fluid such as gas or air can pass when the valve is opened.
The orifices may be equally spaced apart in a single line, or in a plurality of lines or in a regular pattern or series of patterns or pseudo randomly. The spacing between the orifices in the lines, and between the lines, may be the same, the lines may be parallel and the locations of the orifices along the lines may be such that they align in directions perpendicular to the parallel lines, so as to define a matrix of rows and columns of equally spaced apart orifices.
The orifices may exist in a flat plane such as in a large flat plate forming one wall of a manifold containing a fluid.
Preferably the fluid is air, under pressure.
The angle of the plane to the horizontal may be such as to define a support surface for objects located thereon.
The programmable control means may be programmed so as to cause air to be released by orifices below an object, situated thereover, so that the object will be lifted on a cushion of air. Once so lifted, the object can be moved freely, possibly without friction, across the surface.
By providing sensors to detect which of the orifices are in registry with the object and controlling the electrical connections to the electromagnet windings of the valve drives so as to continuously close valves not in registry with the object and open those that are, so the load supporting cushion of air can be made to travel with an object as the latter moves relative to the orifice. By so controlling the valves, air is only permitted to exit through orifices required to generate the load supporting air cushion, and the air flow through the orifice array is significantly reduced relative to air cushion support platforms in which air escapes continually from all the orifices.
An air cushion generating platform constructed to operate as aforesaid also generates less noise than one in which the air is released continuously from all the orifices.
It has been proposed to reduce the air loss from conventional air cushion generating platforms by providing each orifice with a normally closed air check valve, each operable into an open condition by the weight of an object located thereover, due to the downward thrust of the weight acting on vertically protruding probes linked to the valves.
An air cushion support platform constructed to operate in accordance with the invention has the advantage that the valves are individually controllable via the programming, there are no probes protruding upwardly from the surface of the platform, and there is no need for any physical contact between the underside of the elevated object and any part of the platform, once the air cushion has been generated therebelow.
The matrix of orifices may be located in two or more planes, which may be at right angles.
An air cushion conveyor may be constructed using a platform as described which extends in the direction along which objects are to be conveyed, and guides above the surface of the platform define a route therealong for the said objects, which when sensed, are elevated by the air released from thereunder.
The guides may also communicate with the manifold and have orifices therein.
In an alternative arrangement, the orifices may be arranged around a curved surface, and in particular may be in the wall of a passage in a manifold to which fluid under pressure is supplied, and a programme is run on the computer controlled valve opening and closing control means to release air from different ones of the apertures so as to generate a sound wave within the passage.
The latter may be cylindrical or rectangular in cross-section.
The manifold may be annular and have an array of orifices in the internal surface defining the opening therethrough, each controlled by a magnetic drive controlled valve as aforesaid.
The manifold may comprise part of the wall of a passage through which gases or air pass and by controlling the valves pulses of fluid can be injected into the flow of air or gas, so turbulence in the flow can be created or reduced as desired. The fluid is typically compressed air or gas.
Such an annular manifold may form part of the wall of the inlet or outlet of a turbine, or the exhaust or inlet of a jet engine, or the wall of a pipeline carrying gas or air, which may be subject to turbulence.